The Huangshui Creek in Shimen, Hunan Province was seriously contaminated by historical realgar mining area. Discussing the diel variation of arsenic in creeks and the diurnal regularity of algal-arsenic mineral water-rock interaction is of great significance for understanding the migration behavior of arsenic in the watershed and controlling contamination. In this research, the diel variations of arsenic concentration and its hydrochemical parameters were investigated in the field,and the algae species in the Huangshui Creek were separated in laboratory, and the growth of algae and the kinetics of arsenic release from arsenic minerals(realgar) were studied under simulated photosynthesis. The results showed that the arsenic concentration in the creek ranged from 0.8 to 1.1 mg/L, decreased at night and increased during the day, and the arsenic stratification effect was the most obvious at the lake mouth. The changes of temperature, pH value, dissolved oxygen and carbonate content were consistent with those of arsenic concentration, but the changes of chlorophyll a and bicarbonate content were opposite to those of arsenic concentration; The algae species in the Huangshui Creek were abundant and had been separated such as Chlorella, Spirogyra, Scenedesmus, etc. In the experiment, compared with pure realgar, low concentration algae can promote the release of 182.1 mg As (Ⅲ) and 459.3 mg As (Ⅴ) per gram of realgar after 48 hours of action. There was a significant absorption phenomenon in medium concentration algae, and As (Ⅲ) was better than As (Ⅴ). High concentration algae promoted the release of realgar and significantly increased the release of As (Ⅴ), which was 2.9 times that of pure realgar. The experimental results showed that the diel variation can also change the concentration and valency states of arsenic, and the presence of algae played an important role.